The tile sub has just installed floor tiles in our bathrooms (as well as kitchen and mudroom). It all looks fine. However, in one bathroom, the floor squeaks when you walk over it. But it didn't squeak before the tile was applied. This bathroom is on top of an engineered floor with with 3/8 inch plywood on top of 3/4 inch OSB, over trusjoists. The squeak seems to be coming from where the floor tiles butt up against the acrylic shower base. This floor hasn't been grouted yet.

Is this common? Could it be caused by placing the tiles too close to the acrylic shower base? Is it likely to stop squeaking after it's grouted?

What kind of substrate was used for the tile installation?
Was it set directly on the plywood?
Underlayment should have been attatched with screws or staples at a rate of every 3-4" at all seams and 8-10" through the field of each sheet.
Also, is the 3/8" Plywood new?was it allowed to acclimate?could it possibly be delaminating?
Alot of potential problems here.More information would be helpful

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I don't know what kind of substrate was used, but it was the same as used in all other tiled areas of the house. None of them squeak. The substrate was installed directly on top of new plywood. I didn't see how far apart the nails or screws were.

The plywood was down for approximately 2 weeks before the tile was installed. I don't know whether that is long enough to acclimate. Since it has been down only 3 weeks, I doubt it is delaminating, but I'm sure stranger things have happened.

Interestingly, the bathroom vanity cabinet was installed 2 days ago, and the squeaking has diminished somewhat. A builder friend who looked at it over the weekend said he thought the tile is touching the acrylic base, and the noise is most likely caused by the tile rubbing against the base. There is some movement in even the best "engineered floor". He thought the noise may stop when the tile is grouted and when silicone is applied in the joint between the tile and the base.

If the tile isn't hitting the acrylic base, it's probably the 3/8 plywood hitting (more likely to squeak). Also as John B. stated, try going in the shower and walk around, it's very possible that it's coming from the base itself. We just had a similar issue, because the plumber said it wasn't necessary to set the pan in mud. Well it wound up squeaking. We solved the problem by using 1/2" clear glass shower door and panel. Yep, that fixed it.
Not going anywhere now!

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The problem is solved, and I thought those who replied may like to know what fixed it. The tilesetter said the squeak was caused by friction between the thinset and the acrylic base. He knew where to look because he has seen a very similar case once before. The floor squeaked with every step you took inside the bathroom, and even when you walked on the floor just outside the bathroom door, as long as you were on the 3 or so joists holding up the shower pan. He scraped away the thinset between the last row of tiles and the edge of the shower pan, and voila -- the squeak stopped!